1. Field of the Invention
The present invention relates to an endoscope having a channel switching device for switching the communicating states of a plurality of kinds of channels lying through an insertional part for the purpose of such functions as aeration, perfusion, and suction.
2. Description of the Related Art
Generally, in addition to illumination optical fibers, an imaging optical system, and observation optical fibers, many members such as a forceps channel tube that is also used for a suction channel, an aeration channel tube, and a perfusion channel tube are incorporated in an insertional part of an endoscope. For implementing various functions in an endoscope, it is necessary to insert various members in an insertional part of the endoscope. This poses a problem that the insertional part becomes larger in diameter.
Proposed in, for example, Japanese Unexamined Utility Model Publication No. 2-121002 is an endoscope whose insertional part is made thinner by placing a channel switching device in an operation unit.
As shown in FIG. 29, in a channel switching device 200 disclosed in the Japanese Unexamined Utility Model Publication No. 2-121002, a push button 202 formed on the top of a piston 201 is pushed in order to switch channels. The push button 202 is firmly screwed down by means of a male-threaded section 203 of the push button 202 and a female-threaded section 204 in the upper part of the piston 201.
Generally, the foregoing channel switching device included in an endoscope comprises a cylinder unit formed in an insertional part of the endoscope and a valve unit attached to the cylinder unit.
For reusing the endoscope, at least the endoscope and valve unit must be disinfected.
For effective disinfection using a disinfectant solution, it is necessary to expose all the ins and outs of the valve unit to the disinfectant solution. The valve unit is therefore usually detached from the endoscope and then disinfected.
However, since the valve unit has a relatively complex structure, the work of brushing or swinging the valve unit in the disinfectant solution is required to expose all the ins and outs of the valve unit to the disinfectant solution. The disinfection work using a disinfectant solution is therefore time-consuming. Besides, special care must be taken for fear the disinfectant solution be splashed on a human body during the disinfection work.
By contrast, autoclaving is a sterilizing means using hot steam. Since steam penetrates all the ins and outs of a member having a complex structure, the valve unit can be sterilized reliably. Moreover, sterilization can be completed safely and easily for a short period of time. It is therefore preferred that the valve unit be autoclaved.
However, since the known valve unit is not made of a material that is durable to autoclaving, when the valve unit is autoclaved, component parts constituting the valve unit may be damaged.
Moreover, during autoclaving, the valve unit is exposed to a hot steam environment of about 120.degree. to 135.degree. C. The temperature of the valve unit itself reaches about 120.degree. to 135.degree. C. After being autoclaved, when the valve unit is used for endoscopic examination, as long as the valve unit is cooled down to around the room temperature of an endoscopic examination room, a heat-related problem will not arise for an operator. For increasing the patient throughput of endoscopic examination, it is required not to wait until the valve unit is cooled down to the room temperature but to use the valve unit in a heated state in which the temperature of the valve unit is still higher than the room temperature. In this case, depending on the temperature of the valve unit, an operator cannot manipulate the endoscope as he/she intends. In particular, when a metallic member constitutes an outer surface of a valve, there arises a problem that an operator is likely to perceive heat and be hindered from manipulating an endoscope freely.